The Median Tectonic Line (MTL) extends about 900 km parallel to the general trend of the southwest Japan island arc. The central segment of the MTL has been active during the Quaternary. Although the average slip-rate along the MTL is up to several mm a^-1, there is no historical record of destructive earthquakes along it. In order to collect data on the behavior of the MTL during late Holocene times, especially on the timing of seismic events and the amount of displacement during each event, trench studies were conducted on the active segment in central Shikoku in 1984 and 1988. The results are summarized as follows: (1) the latest two seismic events produced by slip on the MTL in central Shikoku occurred during the early 8th century A.D., and between 3250 and 2820 years B.P.; (2) the amount of displacement during the latest event is inferred to have been about 5.7 m; (3) the earthquake magnitude for the latest event is estimated at 7.9 (Richter scale), and a fault-segment trace about 70 km long ruptured during that event; (4) an average slip-rate along the active trace of the MTL in central Shikoku during the late Quaternary is estimated to be 5–8 mm a^-1.